1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having a body with surfaces defined by rubber that contact cooperating pulleys to frictionally transmit forces between the power transmission belt and the pulleys.
2. Background Art
It is known to make power transmission belts, as used on automobile engines, from rubber, such as natural rubber, styrene/butadiene rubber, and chloroprene rubber. In recent years, the demand for energy conservation has dictated that automobiles be made smaller in size. Engine compartments are being made more compact, as a result of which engine components are being placed in closer proximity to each other. There is generally less unoccupied space within the engine compartments, as a consequence of which the temperature in the engine compartments has risen.
In a high temperature environment, such as in the automobile engine compartments, the rubber of the power transmission belt cures and tends to prematurely generate cracks.
Further, engines designed for energy efficient operation tend to experience significant speed fluctuations in operation. As a consequence of this, the tensile forces on the power transmission belt tend to be increased, which may result in significant frictional wear, unwanted generation of sound, and the like.
Additionally, with a halogen-containing rubber, such as chloroprene, dioxine is generated which is detrimental from an environmental standpoint. It is desirable that belts be produced with rubber not containing a halogen.
To avoid the detrimental environmental effects from halogens, various other products have been developed. Ethylene/α-olefin rubbers, such as ethylene/propylene rubber (EPM) and ethylene/propylene/diene terpolymer rubber (EPDM), have been used and exhibit excellent heat resistance and are relatively inexpensive. These polymers do not contain a halogen.
One example of a power transmission belt using an ethylene/α-olefin elastomer, reinforced with a metal salt of α-β-unsaturated organic acid, is shown in Japanese Patent Document No. JP-T-9-500930. This document is a published Japanese translation of a PCT application.
Because the ethylene/α-olefin elastomer has poor water wettability characteristics and is more water-repellant than is chloroprene rubber, the migration of water between the belt and a cooperating pulley during operation may not be uniform. At locations where there is no water residing between the power transmission belt and cooperating pulley surfaces, there is direct contact between the belt and pulleys. However, where water does reside between the belt and pulleys, the coefficient of friction therebetween decreases, thereby potentially causing slippage between the belt and pulley. This tends to generate stick-slip noise.
In the event that there is a high friction coefficient between the belt and cooperating pulley, unwanted noise may be generated during normal operation. Thus, it has generally been desired to control the coefficient of friction to avoid this condition. This has been accomplished by adding a lubricant. However, if a large amount of lubricant is added, there commonly results detrimental adhesive abrasion.